That is not huge - far, far from it. You can pass in the range you want to read into xlsread(), so just pass in a smaller range. If you don't know the range until you've read it in, then read in a little bit more than you think you'd need and check. Otherwise you can use ActiveX to pull over one cell at a time and check it, but honestly I don't believe that will give you any noticeable speed up over just reading the whole thing in and checking it in MATLAB. Or you could read in the whole time column, then check it to see how many rows you need, then read in that many rows from column 5. If you did that, you should use ActiveX because it you used xlsread() to do that, it involves launching Excel twice and shutting it down twice, which is time consuming.
If you're interested, I've attached an ActiveX demo below.
